The evolutionary dynamics of integrons in changing environments.

Area of Science:

• Microbial genetics
• Evolutionary biology
• Genomic instability

Background:

• Integrons are key genetic elements in bacteria, driving genome evolution and facilitating the acquisition of antibiotic resistance genes.
• The evolutionary pressures maintaining integrons, particularly in dynamic environments, remain incompletely understood.
• Integrons act as hotspots for gene cassette recombination, influencing bacterial adaptation.

Purpose of the Study:

• To investigate the evolutionary dynamics and maintenance of integrons in bacterial populations under fluctuating antibiotic selection.
• To model the role of integrase activity in promoting population-level adaptation and genetic diversity.
• To explore the impact of horizontal gene transfer on integron evolution.

Main Methods:

• Development of a mathematical model simulating integron evolution in bacterial populations.
• Competition dynamics between bacteria with and without functional integrase enzymes were analyzed.
• Model parameters explored included varying antibiotic exposure levels and fitness costs associated with integrase activity.

Main Results:

• A functional integrase, despite fitness costs, can be stably maintained in populations experiencing fluctuating antibiotic exposures.
• Gene cassette shuffling by the integrase generates crucial genetic diversity, enabling rapid adaptation to environmental changes.
• Horizontal gene transfer significantly promotes integrase maintenance and can drive the de novo assembly of integrons.

Conclusions:

• Integron evolution is strongly influenced by environmental fluctuations, with stable environments potentially leading to loss of integrase function.
• Adaptive potential is enhanced by intermediate gene-shuffling rates in changing environments.
• Experimental validation of these population biology predictions is warranted to fully understand integron dynamics.